Anesthesia can be considered as an amalgam of several components of which the principal components are hypnotics, amnesics, analgesics, including control of motor activity and of the reactions of the autonomous nervous system.
The aim of present-day anesthesia is to assure:                an induction of anesthesia that is easy and fast        stable haemodynamics and a dynamic balance between analgesia, hypnosis and amnesia during the course of the surgery        muscular relaxation with the aid of curare        a rapid and comfortable recovery from narcosis.        
Intravenous anesthesia (IVA) implies the intravenous injection of several drugs following a pharmacokinetic model. Anesthetic drugs include hypnotics to control hypnosis of the patient, morphinomimetics to control analgesia and curare for muscle relaxation. Traditionally these drugs were applied manually by the anesthetist via syringes. The traditional titration process is time-consuming, labor-intensive and vulnerable to human errors. In addition to that, there is a factor of unpredictability involved which is caused among others by patient variability and which can not fully be taken into account by pharmacodynamic and/or pharmacokinetic models.
The anesthetist is multi-tasked both physically and cognitively during the course of a surgical operation. It is known that human errors are ready to incur upon repetitive tasks such as the constant monitoring of electronic and other signals, the repetitive delivery of drugs via injections etc. Another factor to consider is the fact that serious complications can occur at any time during an operation, which can evolve in a bad direction very rapidly.
It is thus imperative to alleviate the anesthetist's tasks as much as possible, without departing too much from the principle that the “physician knows best”. Better control of IVA and a more comfortable recovery therefrom will also benefit the patient.
The benefit for the anesthetist will be that he can focus his attention on surveillance of the patient and on important events in the surgery such as for instance cardio-respiratory reanimation during a single or double lung transplantation. It is known that the risk of human errors decreases in view of a reliable supportive tool. The human brain is very performing regarding the taking of decisions in complex situations; but when a human being has to survey continuously a monotonous parameter the performance of the human brain falls with an increased hazard for accidents (Schreiber, 1990, Reanim 15: 287-97).
The patient not only benefits from the reduction of risks, there are other advantages linked to better controlled IVA. It has for instance been demonstrated that a fast recovery from a surgical lung transplantation without complications and a fast decoupling from mechanical ventilation apparatuses benefits the patient (Westerlind, JCTVA, 1999, Tran SFAR 2003). A non-justified mechanical ventilation can even be responsible for bacterial colonization of the upper airways, which favors possibly detrimental nosocomial pneumopathies (Chastre and Fagon, Am J Respir Crit Care Med 2002). It has further been shown that a precocious tracheal extubation after a non-complicated cardiac surgery would improve the patient's ventricular performance (Gall et al; 188, J Thorac Cardiovasc Surg 95: 819-27), his cognitive functions and diminishes the occurrence of intrapulmonary shunts (Cheng, 1998, J Cardiothorac Vasc Anesth 12: 35-40). It has also been shown that by subjecting an anesthetic to a monitoring of the depth of anesthesia one is able to obtain an anesthesia more stable with less episodes of hypotension and a faster recovery (Struys anesthesia 2001).
The field of intravenous anesthesia (IVA) has undergone an important progress the last years due to the fact that intravenous (IV) agents with a fast-working and short-lived activity have been put on the market. Certainly the introduction of propofol in the late eighties made this “boost” possible, because in contrast to other hypnotics, like barbiturates and etomidate, propofol is really the best suited intravenous agent for maintenance of anesthesia.
However, in contrast to the rapid progress seen in the field of inhalational anesthetics, introduction of new intravenous drugs has not resulted in the rapid development of new and widely accepted sophisticated intravenous delivery systems. Today, intravenous agents are still commonly administered by manual bolus on a dose/kg basis.
Several new drug delivery systems for intravenous anesthesia have been developed, and introduced during the last 10 years. These are pumps with faster infusion rates and special features, such as “hands-free” bolus delivery function. Despite these sophisticated manually controlled infusion pumps, (T)IVA is sometimes perceived as being more complicated to perform and difficult to control than inhalational anesthesia.
Target-controlled infusion (TCI) apparatuses introduced onto the market comprise an infusion pump attached to a computer (microprocessor). The computer's program contains a pharmacokinetic model, describing the elimination and metabolism of the drug within the body, and pharmacokinetic data for widely different patient populations. The target drug concentration and data specific to the patient undergoing surgery, such as age and body weight, are entered into the system by the anesthetist. From its pharmacokinetic model, the TCI system determines the initial loading dose required to achieve the target concentration and the infusion rate to sustain it, and controls the infusion automatically (http://www.anesthesia.at/anesthesiology/tiva.html).
Entirely computer-controlled delivery systems have been introduced, but were not readily accepted by clinicians. It is however known that the perfusion of hypnotics with the aid of a closed-loop control allows reduction of the total amount of anesthetics being given, allows a faster recovery afterwards and facilitates decoupling from mechanical ventilation machines (Struys 2002). It has further been shown that at least cardiac surgery benefits from TCI (Target Controlled Infusion or computer-aided IVA and choice of anesthetic concentrations) compared to a manual technique (Alvis et al, 1985, Anesthesiology 63: 41-9)
US patent application 2003/0051737 discloses apparatuses and methods for providing computer-assisted titration of the level of sedative, amnesic and/or analgesic drugs in a controlled and a transparent fashion that allows time for manual and/or automatic assessment of the patient's response to changing drug levels. The disclosure of this document is herein incorporated in its entirety by reference thereto, especially with respect to the background of the invention.
Closed-loop control of the bi-spectral analysis of the electroencephalogram, the BIS index, has been the subject of several publications (see e.g. Absalom and Kenny, 2003, Br J Anaesth 90: 737-41).
US application US2002/0169636 discloses a system and method for providing care to a patient, comprising a patient care device having a number of configuration databases stored in a memory in the device. Transferring patient-specific info to the patient care device enables the selection of a specific configuration database from the plurality of configuration databases, the selection being based at least partially upon the patient-specific information. The system is static in the sense that the selected protocol only executes a number of predetermined instructions.
Patent application WO99/10029 relates to an automated medication infusion device. It receives prescription information including information pertaining to a medication prescribed for a patient. The system is only capable of performing predefined tasks. It does not contain any intelligence to propose any other action than merely alerting a clinician when the prescribed medication is found inappropriate to administer to the patient.